Conventionally, it is known that radar apparatuses detect target objects therearound by transmitting transmission signals to the outside, receiving reflection waves caused by the transmission signals, and analyzing the reflection waves with a reception system circuit. Such a radar apparatus is provided with a circulator and a limiter so as to prevent a transmission signal having high signal level from being inputted to the reception system circuit.
The circulator prevents the transmission signal from being inputted to the reception system circuit by switching the flow of the signal. The limiter can protect the reception system circuit even in a case where a transmission signal which could not be intercepted by the circulator is inputted to the reception system circuit, by attenuating the signal having the high signal level. Patent Document 1 and Patent Document 2 disclose arts relating to such a limiter.
A limiter circuit of Patent Document 1 includes a stub that short-circuits with a double wave and a triple wave (harmonic) of a basic frequency. The stub is provided to suppress variation of limit properties of the limiter.
A limiter circuit of Patent Document 2 attenuates a signal having a high signal level by a diode. An open stub that is a transmission line opening at its tip is disposed near the diode. The open stub is provided to adjust variation of junction capacitance value of the diode.